Today, consumers are much more aware of nutrition, particularly dietary fat. This awareness includes a shift toward consumption of low fat products, including low fat milk products. Thus, there is interest in reducing the fat percentage of milk produced by the cow. Milk fat is composed mainly of triglycerides. The mammary cell absorbs the precursors or building blocks for milk production (e.g. the component fatty acids of milk: acetate, B-hydroxybutyrate, and preformed fatty acids) from the circulation. Several reviews have summarized the factors that affect milk fat percentage and yield. Nutrition plays a major role, and certain nutritional practices cause milk fat depression by mechanisms that have not been clearly established.
The milk fat depression (MFD) which occurs when "high concentrate diets" or diets primarily composed of one type nutrient, in this case grains, are fed represent an extreme situation where the rate of milk fat synthesis in an individual cow can decrease by 50% or more. In addition, several other dietary manipulations including rumen active fats, small particle size forage, lush pasture and ionophores all result to varying degrees in decreased milk fat yield. These nutritional situations involve changes in rumen fermentation or metabolism, which are believed to directly or indirectly result in a shortage of lipid precursors at the mammary gland. The actual mechanisms involved in MFD had not been fully explained but several theories have been proposed. These theories can be broadly summarized into two categories: (1) theories which consider the depression to be an indirect consequence of a shortage in the supply of lipid precursors to the mammary gland and (2) those that attribute MFD to a direct inhibition of mammary gland synthesis of milk fat.
The most widely held theory is the glucogenic-insulin theory of milk fat depression. This theory explains the mammary gland shortage of milk fat precursors based on the concept that organs and tissues compete for nutrients. In this competition the uptake of lipogenic precursors by adipose tissue, but not the mammary gland, is responsive to changes in circulating concentrations of insulin. The glucogenic-insulin theory proposes that increased insulin release, which occurs with certain diets (e.g., diets with a large proportion of grains), preferentially channels nutrients to adipose tissue resulting in a shortage at the mammary gland and, thus, milk fat depression.
Other theories suggest that milk fat depression is caused by a direct inhibition at the mammary gland of one or more steps in the synthesis of milk fat. A number of compounds that could be derived from the diet or produced by ruminal fermentation or animal metabolism have been suggested as possible factors that could inhibit milk fat synthesis in the mammary gland. These include trans-octadecenoic acids, methylmalonic acid and cyclopropene fatty acids such as sterculic acid. Direct inhibition of milk fat synthesis by trans-octadecenoic acids (frequently referred to as trans fatty acids; TFA) was first proposed more than two decades ago (Davis and Brown, 1970). Pennington and Davis (1975) further speculated that TFA, resulting from the partial hydrogenation of unsaturated fatty acids in the rumen, were involved in causing MFD with high concentrate diets as well as when polyunsaturated oils were fed. Subsequent studies with cows, goats and mice have demonstrated that TFA produced in the rumen or added to the diet were associated with depressed milk fat production (Astrup et al. 1976; Selner and Schultz, 1980; Wonsil et al. 1994; Gaynor et al. 1994; Romo et al. 1996). Many of these studies used partially hydrogenated vegetable oils as the dietary source of trans-fatty acids and authors concluded that MFD was caused by trans-fatty acids.
U.S. Pat. No. 5,416,115 (hereinafter '115 patent) issued to Erdman et al. in 1995 teaches a method of regulating milk fat by administering trans-fatty acids to lactating cows. The '115 patent defines trans-fatty acids as trans-octadecenoic fatty acids (column 1, line 16-20) and the patent claims to be the first to recognize this connection between TFA and MFD. However, the '115 patent fails to quote much of the prior art (e.g. Davis and Brown, 1970; Pennington and Davis, 1975) and misrepresents other work (e.g. Selner and Schultz, 1980). Further, the '115 patent dismisses the prior work by concluding, "none of these studies have established a causative role between the amount and/or type of isomers of fatty acids ingested by cows and resulting milk fat concentrations." This is interesting because the inventors own scientific work (see review by Erdman, 1996) and the '115 patent also fail to postulate or establish a specific causative role between milk fat depression and specific trans isomers in terms of "amount and/or type of isomers of fatty acids."
The '115 patent claims all trans-fatty acid isomer species (column 12 and 13) as the cause of MFD. However, the inventors of that patent make no distinction between specific trans-isomers in their patent or in their scientific publications (e.g. Teeter et al. 1990; Gaynor et al. 1994; Romo et al. 1996; Kalscheur et al. 1997). In fact, their scientific publications emphasize that MFD is related to total trans-fatty acids (see review by Erdman, 1996). Later data clearly shows that some trans-fatty acids do not cause milk fat depression while others are responsible for some MFD. For example, one can increase trans-11 octadecenoic fatty acid content of milk with no change in overall milk fat percentage. This particular fatty acid predominates in milk fat. When compared to partially hydrogenated vegetable fat (e.g. margarine), butter (a product of milk) contains a wider range of trans isomers (see FIG. 1). Initial data shows MFD was correlated with total trans-fatty acid content of milk fat (Erdman 1996; Griinari et al. 1998). However, using more refined techniques the current invention demonstrates that changes in milk fat content are related to changes in specific trans-isomers and not to total TFA isomers (Griinari et al. 1997, 1998). For example, one can increase trans-11 octadecenoic acid content of milk fat with, no change in overall milk fat percentage. Thus, the broad guesses in the '115 patent about the general nature of trans-fatty acids are just guesses. The patent fails to provide sufficient guidance or enablement to those skilled in the art to determine which compounds cause milk fat depression.